Week 7 Flashcards
Key information about smooth muscle
Cells form layers and line the cavities of hollow organs
Contractions are controlled by the autonomic nervous system
Cells are connected to eath other electrically and mechanically
How are smooth muscles arranged
What does this arrangement allow them to do
Smooth muscles have no sarcomere.
The actin and mysoin filaments are arranged in the form of a lattice around the cell, allowing the smooth muscle to change shape
Dense bodies
Actin filaments attach to the cell via specialised areas in the cytoplasm called the dense bodies
Dense bands
Smooth muscle cells are mechanically connected to neighbouring cells via specialised areas on the membrane called dense bands
How are smooth muscles activated
There are no neuromuscular junctions
The neurotransmitter is released from varicosities
Difference between the activation of a single unit smooth muscle and a multi unit smooth muscle
Single unit - cells are electrically coupled by gap junctions and function as a unit
Multi-unit - cells are not electrically coupked
Each cell needs to be activated by a nerve
How can smooth muscle be activated
Rhythmically by pacemaker potentials or by acute events that pushes the balance of excitation and inhibition above threshold
No sarcomere arrangement means that
Myosin and actin can slide past each other without entering the end of a sarcomere
Role of calcium in smooth muscle
No troponin in smooth muscle so actin binding sites always available
Calcium source is from the sarcoplasmic reticulum or extracelluar sources which activates calmodulin, which activates myosin light chain kinase
Calcium acts on ______________ as opposed to _____________
Thick filaments as opposed to thin filaments
Relaxation of smooth muscle
Happens by myosin light chain phosphatase
If it overwhelms the activation of muscle due to not enough calcium then the muscle will relax and vice versa
What is cardiac output
What is the abbreviation
What are the units
How is it calculated
Cardiac output is the volume of blood pumped out by the heart every minute
Q
ml or l so the units are ml/min or l/min
Heart rate x stroke volume
What happens to CO, HR and SV when workload increases
HR has a linear relationship
SV decreases with more workload as heart has less time to refill
This pushes cardiac output down as workload increases
How does the parasympathetic system slow heart rate
Parasympathetic nerve endings (vagus nerve) secretes the neurotransmitter acetylcholine
How does the sympathetic system increases heart rate
Sympathetic fibres (cardiac nerves) supply the SA and AV nodes and increase HR by releasing norepinephrine
Stroke volume is regulated by two opposing factors
The force by which the muscle cells contract
The arterial pressure against which they have to eject the blood
The force of contraction is regulated by two processes
The length-tension properties of cardiac muscle cells and the effects of hormonal influence on the contractility of cardiac muscle
Starlings law
Increases in venous return
Greater diastolic filling of the heart
Increased chamber elasticity
Increased ejection fraction
Increased force of contraction
Increased stroke volume
To have an increase in cardiac output, what is required
Increase in HR
Increase in SV
For heart rate to increase, what has to happen
Vagus nerve activity decreases
Sympathetic nerve activity to increase
Circulatory epinephrine increases
For stroke volume to increase, what needs to happen
End diastolic volume to increase
Circulating epinephrine increases
Sympathetic nerve activity to increase
What is blood pressure
Driving force for flow in the cardiovascular system
What must blood pressure be?
It must be regulated, so that it is high enough to create flow, but not too high to put excessive stress on the cardiovascular system
Equipment used to measure blood pressure
Inflatable cuff
Pressure gauge
Stethoscope
